Southern growers had alfalfa emerging early. And there were more hatches of weevils. "There were fall-laid eggs, winter-laid eggs, followed by spring-laid eggs," Bailey says.

Weevils are most damaging on first-cutting alfalfa hay crops.

When scouting early, growers may have a hard time seeing the larvae. The youngest larvae stay inside the alfalfa growing tip. By the third and fourth instars, larvae are larger and crawl out to feed on leaves. They become easy to see.

By the time larvae emerged in central Missouri, the pathogens were ready. "Scouting reports the first week of May showed 90 percent kill rates by the fungus."

Biological controls can wipe out alfalfa weevils in 72 hours. Infected weevil larvae become lethargic. Next, the lime-green worms turn a sickly yellow, Bailey says. The larvae die in a short time.

Alfalfa growers who find sick weevils should not spray. The pathogens will do their work.

In southern Missouri, recommended pesticide sprays did not work this spring, Bailey says. "Approved pesticides work best when temperatures reach 60 degrees. The weevils go to work at 48 degrees and that leaves a huge window that favors the bugs."

In a May 2 MU Extension teleconference, regional agronomist Sarah Kenyon said some growers sprayed alfalfa fields four times. Based in Alton, Mo., Kenyon works in counties closest to Arkansas.

Recent scouting shows parasitic wasps were starting work across central Missouri. "The three species of wasps are about 20 percent effective," Bailey says. "They add more potential for killing the pests."

When alfalfa weevil, a foreign pest, first arrived in Missouri, it killed many alfalfa stands. In the last decade, pathogens and parasites caught up with the invaders. Natural controls reduce costs of raising the high-value forage crop.